The present embodiments pertain to a novel imaging member, namely, an imaging member or photoreceptor comprising a binderless overcoat layer which exhibits substantially improved electrical performance, such as low residual voltage or potential and good electrical cyclic stability.
In electrophotographic or electrostatographic printing, the charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as toner. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced or printed. The toner image may then be transferred to a substrate or support member (e.g., paper) directly or through the use of an intermediate transfer member, and the image affixed thereto to form a permanent record of the image to be reproduced or printed. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
The described electrostatographic copying process is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrostatographic printing applications such as, for example, digital laser printing or ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
To charge the surface of a photoreceptor, a contact type charging device has been used. The contact type charging device includes a conductive member which is supplied a voltage from a power source with a D.C. voltage superimposed with a A.C. voltage of no less than twice the level of the D.C. voltage. The charging device contacts the image bearing member (photoreceptor) surface, which is a member to be charged. The outer surface of the image bearing member is charged with the rubbing friction at the contact area. The contact type charging device charges the image bearing member to a predetermined potential. Typically the contact type charger is in the form of a roll charger such as that disclosed in U.S. Pat. No. 4,387,980, the relative portions thereof incorporated herein by reference.
Multilayered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer (sometimes referred to as an “interfacial layer”), a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an optional overcoating layer in either a flexible belt form or a rigid drum configuration. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Multilayered flexible photoreceptor members may include an anti-curl layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
Current long-life overcoat layers have experienced high residual potential and high potential during operation. This poor electrical performance was discovered to be due mainly to the low mobility of charge transport molecules used in the overcoat layers. To avoid the poor electrical performance, and to match the good image quality of those imaging members without overcoat layers, a substantial change in the thickness of the charge generation layer and the charge transport layer must be implemented. However, changes in thickness of the imaging layers lead to other negative effects in the performance of the photoreceptor, such as light shock or increase in cost due to changes in material and production. Thus, there is a need for an overcoat layer that provides similar performance as the current long-life overcoat layers but has much less negative impact on the overall electrical performance of the photoreceptor and requires much less change in thickness of the layers beneath the overcoat layer.
The present embodiments provide for a binderless overcoat layer that imparts long-life service to the photoreceptor and has little negative impact on overall electrical performance of the photoreceptor.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”